In the coming year we propose to continue our investigations on the structural characterization and function of mammalian gene promoters. Appropriate recombinant DNAs carrying segments of DNA that specify RNA initiation sites will be modified by deletion, transposition and base modifications and tested for their activity as promoters. Another aspect of our work will include additional investigations on the structural features of intervening sequences and the role of splicing in the maturation of mRNAs. This year we propose to examine in more detail the steps in mRNA biogenesis that require the presence and splicing of intervening sequences. In addition, we shall evaluate whether different introns can alter the efficiency of mRNA formation.